LOL, I actually went to the nearest IRS office today. It was 5 miles from my residence.
The funny thing is, the IRS office is in the same building as USCIS! I wanted to check out there and add a mailing address with my PO box to my profile, but they already closed.
Anyway, I went the IRS office, got a wait number, got called, and met an IRS agent.
The agent was very nice and polite, and I told him that I came to report my SSN and revoke my ITIN. The process went smoothly, and was told that I will receive a notice from the ITIN department soon.
By the way, I'm planning to visit this building again for the USCIS. I need to notify them my PO box and request them to send me any letters and notices in the future.
I'll let you know my story with them also.